One method and system for operating a fuel lift pump is described in U.S. Pat. No. 5,477,833. This patent describes a method for operating a lift pump in an intermittent manner. Specifically, the method describes shutting of the lift pump off as a way to avoid having a fuel return line. The fuel pump output is routed to an accumulator. The accumulator holds a volume of fuel and releases fuel to the fuel injectors as the injectors release fuel to engine cylinder ports. The lift pump is operated in this arrangement when pressure in the accumulator falls below a predetermined amount. Consequently, fuel pressure at the fuel injectors rises and falls as the fuel pump is operated and as fuel is injected to the engine. An engine controller adjusts fuel injection timing in an effort to compensate for the varying fuel pressure.
The above-mentioned system can also have several disadvantages. For example, while the system may improve fuel efficiency while producing fuel rail pressures used in port injection applications, it may provide little or no fuel efficiency benefit if the fuel pump is required to generate pressures necessary for direct injection applications because the fuel pump may have to be operated continuously to develop higher pressures. Further, the system can cause air-fuel errors when the engine controller makes adjustments to fuel injection timing related to pressure changes in the fuel rail.
The inventors herein have recognized the above-mentioned disadvantages and have developed a system and method that offers substantial improvements.